Conventionally, with respect to an electric guitar amplifier (hereinafter referred to as a guitar amplifier), different types of cabinets (enclosures) are used depending on the music to be played.
Specifically, a cabinet having a structure of open back box baffle, sealed box baffle, bass-reflex baffle, or the like is used, and since high operating efficiency of a speaker is obtained and sound projects forward out of the speaker, the open back baffle is suitable for reproducing such vivid and energetic sound as American sound. On the other hand, in this construction since sound is insufficiently reproduced in bass range, the low-frequency component correction is conventionally performed by an equalizer in an amplifier side.
Then, the sealed box baffle is mainly used for reproducing loud sound such as a live music play, since the operating efficiency of a speaker is low, and in most cases four sets of speakers of 30 cm in diameter are accommodated within the cabinet to be used by a number of musicians producing such hard sound as British rock.
Further, 99% of all the vented baffles (bass reflex) are used in a bass guitar amplifier and the insufficient sound reproduction in bass range is augmented by a bass reflex. The cabinet of bass reflex type is not used as a guitar amplifier. The reason is assumed that the quality of sound in bass range reproduced by a duct may be far from that reproduced by a speaker.
Therefore, either open back box baffle or sealed box baffle is mostly used for a guitar amplifier.
Further, there is conventionally used a cabinet for a guitar amplifier, which is made of thick wood boards of 18 mm to 25 mm in thickness; in order to avoid scratches on the surface and to restrain an unnecessary resonance, the outside surface of which is overlaid with a felt or various kinds of leather (vinyl-leather) similarly to the case of a conventional loudspeaker apparatus; corner sections of which are reinforced by metal fittings; and in which a speaker and an amplifier circuit are accommodated.
When the sound is emitted through the above mentioned conventional guitar amplifier, there arise a problem in which such acoustic expression as variety of timbre, sound echoes and multi-directional emission of sound originally produced by the musical instrument, for example, an electric guitar are not sufficiently reproduced.
When the above-described problem is further studied in relation to a guitar (what is called an acoustic guitar) and an electric guitar, the acoustic guitar has a body of a wooden box which functions as a resonance diffusing box, and emits fundamental tones generated by the strings in simple harmonic motions and also from the body in multiple directions, emits sound of multiple phases having inherent timbre including various tone ratio, in which harmonic tones whose ratio is determined depending on the shape of the body are contained as the containing ratio of harmonics tone attenuates with a lapse of time, thereby producing sound inherent to a guitar.
On the other hand, since the electric guitar emits sound through a guitar amplifier by converting the vibration of metal strings into electric signals using an electro-acoustic transducer (pick-up) which is placed under the strings on a resonance body of either resonance box or single board, it is difficult to achieve a sound expression inherent to a musical instrument such as variety of timbre, sound echoes and multi-directional emissions of sound, which are produced by resonance diffusing box such as the acoustic guitar.
In other words, since the vibration of metal strings is picked up at a single point and is emitted in a single direction as a sound energy, a sound source is considered to be completely different from that of an acoustic guitar, in which every part of the body emits sound in multiple directions.
Even if an electric guitar is equipped with a resonance box, the sound generated by the resonance box is considerably low in comparison to magnified sound from a guitar amplifier, and therefore it is considered to be impossible to reproduce all of its inherent expression.
However, since the strings of the electric guitar are influenced by composite harmonic tones which are generated by a resonance board, electric signals converted from the vibration of metal strings carry contents of various harmonic tones and sound echoes close to a live musical instrument.
Accordingly, the object of the present invention is to provide a loudspeaker apparatus, which functions as a guitar amplifier (including a speaker, a cabinet and an amplifier), capable of reproducing sound similar to that of a live musical instrument, in which electro-acoustic signals electrically converted from vibration by a pick-up become sound with intrinsic features of an acoustic guitar, such as various harmonic tones, echoes and multi-directional emissions of acoustic energy.
As described above, a cabinet used for the guitar amplifier is mostly of either open back box baffle, sealed box baffle or bass reflex and is made of non-resonant solid thick wood boards; and since sound energies are emitted in concentric waves from the center of a point where the speaker is attached, there is no sound emission similar to those emitted from the body of an acoustic guitar, and in addition, a high frequency range is restrained by a felt or the like overlaid on the surface of the cabinet and sound signals are emitted as a reproduction sound close to electric signals, which contains less harmonic tones. Accordingly, the second object of the present invention is to improve a cabinet (synonymous with an enclosure, a speaker box, a casing or a housing) so as to obtain a loudspeaker apparatus, in which multi-directional emission of sound from the cabinet is increased, sound in a high frequency range is not to be absorbed, the capability of reproducing sound in a high frequency range (harmonic tones) is enhanced and sound energies of middle and low frequency range is capable of being emitted in multiple directions.